Just updated the question removing the "Amazon" from title, but keeping it on the description, since it could be an important information for suggestion on Amazon solutions for scheduling tasks.
–
cawecoyApr 24 '14 at 18:57

I tried to create cron jobs with exec, but it didn't work. I think it's because of the username you said :S
–
cawecoyApr 24 '14 at 18:59

I found a great class that does what I want (look at my answer). The main solution was something like the following php code: shell_exec('echo "'.$all_cron_jobs.'" | crontab -');. Simple as that.
–
cawecoyMay 12 '14 at 19:55